Since its inception in 1968, heart transplantation has developed into a therapeutic possibility for patients with end-stage cardiac failure. More than 230 transplantation centers have been established throughout the world, and more than 25,000 patients world-wide have undergone heart transplantation (Kaye, 1993, J. Heart Lung Transplant. 12:541-548). Initially, the major drawback following transplantation was the risk of rejection due to the recipient's own immune system. Although the introduction of immunosuppressive agents, notably cyclosporin, has improved the situation, rejection still remains an important challenge for the treatment of transplantation patients (Oyer et al., 1991, Transplant. Proc. 15(Suppl. 1):2546-2552; Burdick and Kittur, 1991, Transplant. Proc. 23:2047-2051).
Acute rejection remains the major cause of morbidity and mortality following human heart transplantation, and is a severe complication or cause of death in other organ transplantation procedures as well. Two major analytical methods are used to evaluate the state of the transplanted heart (Carrier, 1991). The first method involves evaluation of the induction and expression of immunity against the allograft, for example cytoimmunological monitoring of lymphocytes, and analysis of cellular markers (such as soluble CD-4, CD-8, IL-2 receptor, and T cell antigen receptor), cytokines, and lymphokines associated with lymphocyte activation. The second method involves evaluation of the graft function and status, e.g., by echo doppler, radiologic imaging, and magnetic resonance imaging. The first grading system of acute cellular rejection was introduced in 1973 (Caves et al., 1973, Thorac. Cardiovasc. Surg. 66:461-466). A grading system which currently is in general use is based on the degree of infiltration and myocyte necrosis in endomyocardial biopsies and uses the grades 0, 1A, 1B, 2, 3A, 3B and 4 (Billingham et al., 1990, J. Heart Transplant. 9:588-593). While there is considerable disagreement as to which methods are the most accurate prognosticators of heart status after transplantation, it is commonly agreed that all of the approaches used in the art inadequately predict all, or even a satisfactory number of, cases of acute rejection early enough (Billingham, 1990, Prog. Cardiovasc. Dis. 33:11-18; Carrier, 1991, Can. J. Surg. 34:569-572; and Burdick and Kittur, 1991, Transplant. Proc. 23:2047-2051). In particular, the amount of lymphocytic infiltrate detected pathologically may not be helpful in diagnosing rejection episodes and determining the need for treatment (Auchincloss and Sachs, 1993, "Transplantation Graft Rejection," in Fundamental Immunology, Third Edition, William E. Paul editor, Raven Press: New York, pp. 1099-1141, 1129). Similarly, the level of soluble IL-2 receptors, while indicative of immune activation, is associated closely with viral infection as well as organ rejection. Since viral infection represents one of the common differential diagnoses at the time of transplant organ dysfunction, such nonspecific assays for immunologic function suffer from an inability to determine the target of immune activation (Auchincloss and Sachs, supra, p. 1129).
Recently, Ferran et al. (1993, Transplantation 55:605-609) analyzed the expression of the cell adhesion molecules ELAM-1, VCAM-1, and ICAM-1 on myocardial biopsy specimens from 16 cardiac allograft recipients either for routine monitoring or for the investigation of suspected rejection. Three to six sequential biopsies taken at one-week intervals were analyzed by means of conventional histology and immunohistochemistry (Ferraln et al., supra). They found that the biopsies of 7 patients who did not develop rejection during the study were negative for VCAM-1 and ELAM-1, although faint ICAM-1 staining was present on capillaries, reflecting constitutive expression. In 3 patients with clear-cut clinical and histological signs of acute rejection, intense VCAM-1 and ICAM-1 expression was detected, but ELAM-1 was undetectable in all three cases. In four out of 6 patients who developed acute rejection during the course of the study ELAM-1 and VCAM-1 were expressed one or two weeks before the histological diagnosis of rejection, and only VCAM-1 expression was observed in the other two. Also, in the four patients, ELAM-1 expression was short lived and had disappeared by the time CD3 cellular infiltrate was detected, thus extending in vivo the finding that ELAM-1 expression is usually transient in vitro. Based on these results, the authors suggested that both ELAM-1 and VCAM-1 expression may have a predictive value in acute cardiac allograft rejection, adding that since ELAM-1 expression is transient, careful monitoring with a close sampling interval would be necessary.
ICAM-1 is a marker of immune activation and endothelial damage, but has not been found to be correlated with cellular rejection as assessed by endomyocardial biopsy (Ballantyne et al., 1994, J. Heart Lung Transplant. 13:597-603). Markers of myocardial damage such as creatine kinase MB and myoglobin have not been useful in identifying rejection in heart transplanted patients (Ladowski et al., 1992, Chest 102:1520-1; Jennison et al., 1992, Circulation Suppl 86:1-844; Gash et al., 1994, J. Heart Lung Transplant. 13:451-454).
Patients often go through unpredictable phases of varying degree of rejection.
Early diagnosis of the approach of rejection is essential to keep the patient in a state of stable non-rejection and avoiding advanced states of tissue destruction, while keeping the level of immunosuppressive therapy as low as possible to avoid onset of opportunistic infections.
Rejection phenomena are not limited to heart allografts. All organ transplants are subject to rejection (host versus graft disease). In addition, rejection-like events accompany graft versus host disease (where transplanted leukocytes and lymphocytes attack the host tissues) and autoimmune disease (e.g., rheumatic fever, in which the heart is the target of an autoantibodies and auto-reactive lymphocytes). In all cases, while aggressive immunosuppression is indicated to reverse or correct the immune reaction, the associated danger of facilitation of opportunistic infections constrains the use of immunosuppression.
Accordingly, there is a need in the art for a highly accurate prognostic indicator of the likelihood of onset of organ rejection. There is a further need in the art for a diagnostic indicator of the grade of cellular rejection (as in Billingham et al., supra).
There is a further need in the art for identification and detection of a specific and sensitive marker of organ rejection to direct administration of immunosuppressive agents, thus avoiding the need to maintain constant immunosuppression in a subject, and allowing for aggressive immunosuppressive therapy to head-off a rejection episode.
The citation of any reference herein should not be construed as an admission that such reference is prior art to the instant invention.